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  #1  
Old 26-08-2017, 09:55 PM
Torque Torque is offline
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TH350 with high powered big block

Anyone using or has used a powerful big block (500hp+) motor with a TH350 transmission? Any issues? I don't really want to fork out for a 400 if I don't have to.
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  #2  
Old 27-08-2017, 08:32 AM
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BlackoutSteve BlackoutSteve is offline
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If you are expecting to fit standard TH350 behind a BBC, forget it.
Any TH350 can be (will have to be) modified to be able to handle the additional torque.
A TH400 in relatively stock form will be OK, hence why the factory put TH400s behind BBCs and not TH350s.
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Old 27-08-2017, 10:11 AM
Torque Torque is offline
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Sorry I should have clarified. The car has a TH350 in it and I have the cheaper option to repair the existing transmission or upgrade at a much higher cost. Some say the 350 is fine whilst others say an upgrade is the only option.
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Old 27-08-2017, 10:19 AM
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Play it safe/smart, throw your cabbage at a th400 or a Glide.
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Old 27-08-2017, 10:58 AM
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BlackoutSteve BlackoutSteve is offline
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From experience..
I persisted with a stock TH350 behind what was maybe a 450-500hp BBC years ago. I blew the rear sprag in it twice, had it repaired both times and rather than waste even more money, went for a 'Glide that is now comfortably handling 700hp. A decent TH400 will easily do that too.
Go-fast parts for TH350s weren't available back then (late 90's) but they are now if you are prepared to spend the money.
Unless you build that TH350 to deal with the torque, you will be removing it shortly to either replace a stack of broken parts, kamikaze'd by what breaks or replace the whole thing with a trans capable of the task.

In stock and even lightly modified form, TH350s are p!ss weak.
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  #6  
Old 27-08-2017, 08:26 PM
Geoff 4 Geoff 4 is offline
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The T350 will last, if you do some important mods. Replace all bushes.
For reasons known only to GM, they didn't know that when you drill a hole in something, you weaken it............
The intrrmediate roller clutch is the weak link, & you can buy the 'hardened' version that others speak of. Only problem is that it still has the oil holes, which is where they break....
If only GM had ground some grooves in the side for oiling, instead of drilling holes, these things might have been ok.....

The only way to ensure reliability is to buy the one piece direct clutch drum with inter sprag clutch. The rigid one piece drum assy stops the sprag clutch from flexing....& breaking.
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Old 29-08-2017, 06:59 PM
Geoff 4 Geoff 4 is offline
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Was looking at a Pontiac forum earlier. 505 Pontiac engine, 3600 lb car weight, runs 9.90s with a T350.
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Old 29-08-2017, 07:18 PM
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Quote:
Originally Posted by Geoff 4 View Post
The T350 will last, if you do some important mods. Replace all bushes.
For reasons known only to GM, they didn't know that when you drill a hole in something, you weaken it............
The intrrmediate roller clutch is the weak link, & you can buy the 'hardened' version that others speak of. Only problem is that it still has the oil holes, which is where they break....
If only GM had ground some grooves in the side for oiling, instead of drilling holes, these things might have been ok.....

The only way to ensure reliability is to buy the one piece direct clutch drum with inter sprag clutch. The rigid one piece drum assy stops the sprag clutch from flexing....& breaking.
Quote:
Originally Posted by Geoff 4 View Post
Was looking at a Pontiac forum earlier. 505 Pontiac engine, 3600 lb car weight, runs 9.90s with a T350.
OP, the oracle above has spoken........you're golden with your th350

Just make sure that one of your thumbs is operational
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Last edited by rodent; 29-08-2017 at 07:21 PM..
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Old 30-08-2017, 10:50 PM
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Im running a TH350 behind a 455ci Pontiac that makes 556hp.

They can be built strong just tell your trans builder what you want.

I weighed up the options, new tailshaft, kickdown, shifter etc and decided the TH350 was the way to go.
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Old 01-09-2017, 08:26 AM
Torque Torque is offline
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Turns out the car (it's a new car for me) has a TCI Streetfighter TH350 which is a toughened version of the stock 350. The car is a manualised auto which according to TCI can also be run as a full auto without changing the valve body. The original fault was a simple fix and due to the vehicle being unused for such a long time. Obviously I'll stick with the TCI Streetfighter and see how it goes. Thanks for all the suggestions. ����
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